1. Field of the Invention
The present invention relates to a mass spectrometer and a method of mass spectrometry.
2. Discussion of the Prior Art
Mass spectrometers are known having an RF ion guide which comprises a multipole rod set wherein ions are radially confined within the ion guide by the application of an RF voltage to the rods. The RF voltage applied between neighbouring electrodes produces a pseudo-potential well or valley which radially confines ions within the ion guide.
RF ion guides are used, for example, to transport ions from an atmospheric pressure ion source through a vacuum chamber maintained at an intermediate pressure e.g. 0.001-10 mbar to a mass analyser maintained in a vacuum chamber at a relatively low pressure. Mass analysers which must be operated in a low pressure vacuum chamber include quadrupole ion traps, quadrupole mass filters, Time of Flight mass analysers, magnetic sector mass analysers and Fourier Transform Ion Cyclotron Resonance (“FTICR”) mass analysers. The RF ion guides can efficiently transport ions despite the ions undergoing many collisions with gas molecules which cause the ions to be scattered and to lose energy since the RF radial confinement ensures that ions are not lost from the ion guide.